A rotation detecting apparatus detects, for instance, revolutions of an engine mounted on a vehicle, and rotations of a rotator provided in a general-purpose machine. More specifically, the rotation detecting apparatus is capable of detecting rotation modes of the rotor by utilizing changes contained in resistance values of magnetic resistance elements.
Conventionally, as the above-described rotation detecting apparatus capable of detecting the rotations by utilizing the resistance value changes in the magnetic resistance elements, for example, a rotation detecting apparatus described in Japanese Laid-open Patent Application No. H07-333236 is known.
This rotation detecting apparatus includes a magnetic resistance element and a biasing magnet. The magnetic resistance element and the biasing magnet are stored into a case member. In this rotation detecting apparatus, a tip portion of the biasing magnet abuts against an inside bottom plane of the case member, and further, a tip portion of a molding member containing a magnetic sensor chip abuts against a projection portion formed on this inside bottom plane, so that such an “M-to-M distance” is determined, and this “M-to-M distance” corresponds to a distance between the magnetic resistance element and the biasing magnet. In other words, in this rotation angle detecting apparatus, deflection angles of the above-explained magnetic vectors which also contain a relationship with a rotor via a projected length of the projection portion formed on the inside bottom plane of the case member are optimized, namely, a sensing sensitivity as to the rotation angle detecting apparatus is optimized.
On the other hand, although the deflection angles of the magnetic vectors corresponding to the sensing sensitivity for the rotation detecting apparatus can be adjusted based upon the above-described M-to-M distance, the projected length of the projection portion formed on the case member must be changed in order to adjust this sensing sensitivity of the rotation detecting apparatus. As a result, in such a case that the above-explained M-to-M distance must be changed in view of unavoidable reasons and this distance change is caused by, for example, the shape of the rotor for the rotation detection mode, the case member itself must also be changed in view of the unavoidable reason. That is, for instance, parts numbers as to these changed case members must be increased, and also, a total number of metal molds must be unavoidably increased which are required to mold these changed case members. In an actual case, such an adjustment itself that the deflection angles of the magnetic vectors are adjusted only by changing the above-described M-to-M distance may cause some limitations. That is, a freedom of designing as to the rotation detecting apparatus is low, and the range for adjusting the deflection angles of the magnetic vectors is restricted in the practical field.